Reef nutrition

PAR meter #1 vs #2 measurements

JVU

BOD
Staff member
By chance I recently had PAR meter #1, and now have #2. Was able to measure the same spots in my tank with the same light settings for a good comparison.

#1 is the Apogee MQ-200 PAR meter. Been our standard workhorse since 2013. Not specifically for in-tank use, so you need to multiply values by the 1.08 correction factor to get the PAR underwater.

#2 is the Apogee MQ-510 PAR meter, new, the main difference is more inclusive reading in the bluer spectrum that is popular now, and it is specific to underwater use so the correction factor is built-in.

The queue has been quite short for #1 now that #2 has been out. I thought I’d share my findings for those of you not sure which to use.

Using both, I definitely get the feel that they are reliable and consistent in their readings. Both now have a nice carrying case and long handle. The readout part is almost the same.

I recently posted my PAR numbers from #1 in my tank journal, before the 1.08 CF. I measured each spot again with #2, and compared the readings with #1 (with CF). One thing to caution is that although these meters give you an exact number, extreme accuracy isn’t the goal here, it is ballpark measurement. Even with that in mind, you will be surprised by the numbers overall and in certain areas of your tank if you haven’t ever checked. Light reflected from inside our tank to our eyes isn’t a good correlation with PAR meter readings at all.

My whitest setting is midday, 75% color setting and 80% intensity in Kessil lingo. At this setting, the #1 vs #2 readings were very consistent, essentially the same accounting for how they jump around a bit even with nearly-still water surface.

Testing a much bluer setting that I also use during the day, 40% color and 80% intensity, #1 was definitely measuring less PAR than #2, as expected due to sensor limitation. I didn’t meticulously do the math, but #1 was around 15-25% less or so, significant. When I went even bluer to 15% and 0% color which I use early morning and late evening, the numbers were less consistent and really significantly under-measuring with #1.

I also noticed that #2 readings didn’t drop off much as I went bluer with the same intensity, which is helpful to know. For example, if you normally run bluer you can check with same intensity but whiter for a more accurate reading with #1.

So my takeaway is that if a relatively whiter setting is part of your high-intensity period, then both meters will give you good results and #1 is probably easier to get your hands on quickly. If you run blue but can adjust whiter for measurement at the same intensity, then either would be good. If you run bluer all day and want to check that directly, you should wait for #2.
 

Flagg37

Supporting Member
Sounds like I need to get the 2nd one.

Thanks!


Sent from my iPhone using Tapatalk
That’s just it, he’s saying you shouldn’t need the second one. Just turn your lights to white at the same intensity and it will read them properly. Do you have t5’s where you can’t simply switch to white?
 

bluprntguy

Supporting Member
That’s just it, he’s saying you shouldn’t need the second one. Just turn your lights to white at the same intensity and it will read them properly. Do you have t5’s where you can’t simply switch to white?
I can't imagine who falls into the "if you run blue but can adjust whiter for measurement at the same intensity" category.

There are a few reasons why you can't just turn your LED lights to white and get similar results:
  • The number of whites vs. blues aren't usually equal in most fixtures. Example: turning 4 white LED's to 85% is different than turning 10 blue/royal blue/violet/UV LED's up to 85%.
  • Different color LED's have different efficiencies in converting electricity to light. Even if you could adjust for the number of LED's in your fixture, you'd have to contend with figuring out the efficiency of each one.
  • Even if you could figure both of these out sometime before PAR Meter #2 becomes available, it seems like a serious PITA to actually accomplish making the light whiter but the EXACT same intensity in order to use the PAR meter #1 to measure it.
I think most people are using the PAR meter to easily find the PAR levels during various times during their light cycle, and they are apparently willing to wait for the one that's more accurate in order to do that easily.
 

Rostato

Supporting Member
I agree. If you run mostly blue you should use #2

I had used #2 in the past and used #1 to check my tank after switching lights and I got less PAR than I was expecting even with the correction factor.

2 of my SPS have bleached since. I thought I was good, but this really helped.

I should have used acclimation mode.
 

Flagg37

Supporting Member
I can't imagine who falls into the "if you run blue but can adjust whiter for measurement at the same intensity" category.

There are a few reasons why you can't just turn your LED lights to white and get similar results:
  • The number of whites vs. blues aren't usually equal in most fixtures. Example: turning 4 white LED's to 85% is different than turning 10 blue/royal blue/violet/UV LED's up to 85%.
  • Different color LED's have different efficiencies in converting electricity to light. Even if you could adjust for the number of LED's in your fixture, you'd have to contend with figuring out the efficiency of each one.
  • Even if you could figure both of these out sometime before PAR Meter #2 becomes available, it seems like a serious PITA to actually accomplish making the light whiter but the EXACT same intensity in order to use the PAR meter #1 to measure it.
I think most people are using the PAR meter to easily find the PAR levels during various times during their light cycle, and they are apparently willing to wait for the one that's more accurate in order to do that easily.
I’ve only ever run Kessils and they have a color adjustment (to change from white to blue) and an intensity adjustment. I guess I assumed that other brands would have a way to keep the same intensity and just adjust the color.
 

JVU

BOD
Staff member
I can't imagine who falls into the "if you run blue but can adjust whiter for measurement at the same intensity" category.

There are a few reasons why you can't just turn your LED lights to white and get similar results:
  • The number of whites vs. blues aren't usually equal in most fixtures. Example: turning 4 white LED's to 85% is different than turning 10 blue/royal blue/violet/UV LED's up to 85%.
  • Different color LED's have different efficiencies in converting electricity to light. Even if you could adjust for the number of LED's in your fixture, you'd have to contend with figuring out the efficiency of each one.
  • Even if you could figure both of these out sometime before PAR Meter #2 becomes available, it seems like a serious PITA to actually accomplish making the light whiter but the EXACT same intensity in order to use the PAR meter #1 to measure it.
I think most people are using the PAR meter to easily find the PAR levels during various times during their light cycle, and they are apparently willing to wait for the one that's more accurate in order to do that easily.
It’s completely straightforward with Kessils, so I guess that‘s the answer to your question. Maybe it doesn’t work well with other brands that give you more (too much IMO) control over every diode.
 

Chromis

Supporting Member
Great write-up. I have similar observations that if you run Kessils in the daylight-ish spectrum it doesn’t matter how you measure PAR but if you are running Radions on UV-blue there is some discrepancy between sensors.
 
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